The nervous system serves as the body's control center and electrical-chemical communications network. The nervous system processes countless bits of information and generates appropriate reactions by sending electro-chemical impulses through nerves to the body's effector organs, such as the muscles and glands. The nervous system is comprised of the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which connects nerve processes to effectors and receptors.
The PNS has two parts: the somatic nervous system (SNS) and the autonomic nervous system (ANS). The SNS, or voluntary nervous system, enables humans to react consciously to environmental changes. This system controls movements of “voluntary” muscles. The ANS, on the other hand, regulates “involuntary” organs and maintains normal internal function. The efferent portion of the ANS is divided into sympathetic and parasympathetic systems. The sympathetic nervous system is affiliated with stress and the “fight or flight response” to emergencies, while the parasympathetic nervous system is affiliated with relaxation and the “rest and digest response.”
Autonomic balance reflects the relationship between parasympathetic and sympathetic activity and may provide an indication of a body's well-being or lack thereof. Changes in autonomic balance are reflected in changes in heart rate, heart rhythm, contractility, remodeling, inflammation and blood pressure. Changes in autonomic balance can also be seen in other physiological changes, such as changes in abdominal pain, appetite, stamina, emotions, personality, muscle tone, sleep, and allergies, for example.
The use of nerve stimulation for treating and controlling a variety of medical, psychiatric, and neurological disorders has seen significant growth over the last several decades, including for treatment of heart conditions, epilepsy, obesity, and breathing disorders, among others. For instance, modulation of the autonomic balance with neural stimulation has been shown to be possible and have positive clinical benefits, such as protecting the myocardium from further remodeling and predisposition to fatal arrhythmias following a myocardial infarction (MI). However, stimulation of the nervous system, such as the ANS, can have unintended consequences (i.e., side-effects), including altering one's voice, coughing, pharyngitis, paresthesia, dyspnea, nausea or laryngismus, and may require considerable amounts of artificially-generated energy.
What is needed is a system and method for stimulating a selected nerve target within a nerve trunk in a way that maximizes, or nearly maximizes, the efficacy of a therapeutic stimulation signal when treating a particular disorder. What is further needed is a stimulation system and method having the ability to monitor undesirable stimulation side-effects and minimize or abate the same by changing the stimulation electrode vector combination or stimulation signal parameters used.